Speedometer of the eddy-current type



April 3, 1928. 1,664,406

w. ERFURT H SPEEDOMETBR OF THE EDDY CURRENT TYPE 1166 March 11. 1926 Patented Apr. 3, 1928.

- um111312sfm'rrsswILHELm EREU'BTI or. BERLIN, GEBMANZ,;ASSIGNOB.TO.-DEUT.A+WEBKE, voIm'ALs.

DEIITSCHE- TACHOMETERWERKE. G.. M: 11,02 BERLIN; GERMANY 'srE'Enom 'mR 01mm EDDY-CURRENT TYP Application-filed March 11; 1925*,ser1ariwo. 14-;851, aml'iifGermany 'March"29 192 4.'

111* speedometers of the eddy current type this kind: are known 4 in which the armature is eitherbell shaped or drum shaped and also. ofdisc shape construction. In. the first case, the bell shaped armature calls for" a requisite-height of the instrument; While; in the; case of disc shaped. armatureson'ly sets of magnets have so; farheen:known='which are: composed" of ai'number" of individual magnets occupyingin the" axial direction a space which represents a considerable mul tipleof thetliickness of the armature;

In" tachometers" it is" generally speaking,

desirable to have as flat a construction: as

possible particularly in instruments which are designed? to" accommodate additional counting mechanism. or odometers, such as for example, speed? indicators'for automobiles: Iirsuclicases, therefore, andih-particular in edc'lyicurrent' tachome'ters, aTma'g netv of, reduced dimension" particularly in vertical direction is of particular advantage. An eddy current tachometer p rovided with such a, magnet Wlierein' all lines of force penetrate the armature between the polesin asingle airgap, the armature being, of disc shape capable of'easy manufacture and of being rea'dilyhalanced; forms thefsuhject of? the present invention; Further advan: tages .ofthe magnet reside-inthe fact that it can heproduced'in a; most simple manner, for example, by stamping, and that even at high-rotary speeds it; is practically, speaking liable tono deformation, and! further that for gauging purposes its effective magnetic field may be varied'within wide vlimits by simplemeans. e

1" illustrates in an elevationalview the gauging mechanism andfthe; essential parts of a speedometer of'the eddy current type according tothis invention. 7

edeby the weiglitiof the mag Fig 21s: a plain view; thereof omitting; however; the=pointer and-{counterspring:

Fig 3 is anaelevational view-of a'modi fied formof magnet Fig; 4 is a plair view thereofi Figsfiiis an elevational -vi'ew of a'further modified form of 'magneti Figs 6 is=a plan view tliereoff Fig. 7 is a plan v-iew of astill further modified formof'magnet.

l is the 1nagne-t"\vhich.;.isflat and disc shaped havingone shank-'- provided with" a pole shoe 2. The effective magnetic field penetrating the disc shaped" armature-4pxtends between the pole shoe 2 and the was of the" other 1 flat: shank ofthemagnet. The arma-ture l has its -ax isor shaft 5 jou-rnalled betweenn pointss' The magnet 1* is rigidly is exerted' on the armature in opposition to the: spring '8:- Theamplitude of the armas tur'e is prop'ortionate" to the number of revolutions of? the magnet, and" can in the usual manner, I he read on a division' accord; ing to the position' of the pointer 9 thereon; As will be understood a magnetsoshaped can be readily and 'chea-ply' produced from ordinary magnet steel sheets by stamping. The centrifugal forces occurring during r0- tat'ion are-taken up bythe greatest momentum of resis'tanceof its cross section, rwhich inview oftlie fiat shape is. so considerable as to practically exclude: all' deformation.

For gauging" purposes themagnetic field HBtWQQHitllBPOlS 2'- and 3'niay be varied by means off'aset screw 10 which is screwed into a lug 11" on the magnet carrier 7 projecting over the'edgepfthe armature 4. In rotatingthe"head off the set screw '10, the upper" pole shoe 2:iscaused to approach or to move away" from; the magnet pole 3 in which action" the; magnet can readily yield in this way, only a very slight partial displacement of the mass takes place in axial direction, the balance of the magnet weight in regard to its axis of rotation remaining, however, the same.

Thejadditional pole shoe may be dispensed with i'f'as shown in Figs. 3 and L the magnet 12 at the place indicated at 18 is cranked up and about the discshaped armature (not shown) so that its pole let comes to lie above the latter opposite the pole 15.

Fig. 4 illustrates moreover how the magnet 12 is providedwith an inwardly projecting lug 16 containing a bore 17 enabling it to be directly secured on its drivingshaft, thereby dispensing with a separate magnet carrier as shown at? in Figs. 1 and 2.

It is within the scope ofthis invention to shape the magnet asshown, in Figs. 5 and 6. In this case the magnet has the form of a flat closed ring 18 which is provided with a diametral web 19. The end of this web as shown at 20 forms the pole located below the armature disc, whilethe pole above it as shown at 21 is produced by offsetting the magnet ringat the points 22. By means of a bore 23 in the web 19 this magnet 18 may likewise be readily secured on its driving shaft. V

The ring shaped disc of the magnet may, however, be also quite flat, that is to say, have nooifsetting if as shown in Fig. 7 a poleshoe 25 is secured to the magnet opposite the end of the web 24, which pole shoe is offset about the edge of the armature disc;

lclaim: 1. A magnetic speedometer comprising a V flat disc-shaped magnet and having one pole thereofin the plane of the magnet; a pole shoe mounted on said magnet and forming the other pole thereof, the free .end of the pole shoe being in a plane which is parallel to the plane of the magnet; and an armature for thepoles which is adapted. to be rotatably mounted in a, plane which is parallel to and between the planes of the pole shoe and the-magnet.

2. A magnetic speedometer comprising a flat disc-shaped magnet and having one pole thereof in the plane of the magnet; a pole shoe mounted on said magnet and forming the other pole thereof, the free end of the pole shoe being in a plane which is parallel to the plane of the magnet; means for rotatably mounting said magnet; and an armature for the poles which is adaptedto be rotatably mounted in a plane which is parallel to and between the planes of the pole shoe and the magnet.

3. A magnetic speedometer comprising a flat disc-shaped magnet and having one pole thereof in'the plane of the magnet; a pole shoe mounted, on said magnet and forming the other pole thereof, the free end of the pole shoe being in a plane which is parallel to the plane of the magnet; an armature for the poles which is mounted in a plane parallel to and between the planes of the pole shoe and the magnet; and means for rotatably mounting said armature.

i. A magnetic speedometer comprising a shaftadapted to be driven; a magnet car- :rier mounted on said shaft; a flat disc-shaped magnet mounted on said carrier and having one pole arrangedin the plane-thereof; a pole shoe mounted on said magnet and forming the other pole thereof, the free end of the pole shoe being in a plane which is parallel to the plane of the magnet; a second shaped magnet mounted on said carrier and having one pole arranged in the plane thereof; a pole, shoe mounted on said magnet and forming the other pole thereof, the free end of the pole shoe being in a plane which is parallel to the plane of the magnet; a sec: ond shaft; adisc shaped armature mounted on said second shaft and being adapted to rotatein a plane which is parallel to and between the planes of the pole shoe and the magnet; a spring for controlling the rotation of the second shaft; and means for indicating the extent of movement of the second shaft. 7 v

6. A magnetic speedi'nneter comprising shaftlad'apted to be driven; a magnet carrier mounted on said. shaft; a flat disc-shaped magnet mounted on said carrier and having one pole arranged in the plane thereof; a pole shoe mounted on said magnet and forming the other pole thereof, the free end of the pole shoe beingin a plane which is parallel to the plane of the magnet;'a second shaft; a disc shaped armature mounted on said second shaft and being adapted to romm in a plane which is parallel to'and be- I securely mounted on said shaft; a; flat di'scshaped magnet mounted on said carrier and of, saidplane being at right angles to the axis of the shaft; a pole shoe mounted on said magnet, and, forming the other pole thereof, the free end-of the pole'shoe being having one pole arranged in the plane'therein a plane which is parallel to the plane of the magnet; a second shaft; a disc-shaped armature mounted on said second shaft and being adapted to rotate in a plane which is parallel to and between the planes of the pole shoe and the magnet; a set screw for ad- .7

justing the position of the pole shoe relative to the pole of the magnet; a spring for controlling the rotation of the second shaft; and

a pointer mounted on the second shaft and 10 In testimony whereof I afiix my signa- 15 ture.

WILHELM ERFURTH. 

